The apparatus of this invention is an improvement in the circuits conceived by Slobodan Cuk, et al., as described, for example, in Electronic Design News, May 20, 1979, on pages 54, et. seq.
A description of the prior art may also be found in "A New Optimum Topology Switching DC-to-DC Converter" by Slobodan Cuk and R. D. Middlebrook in IEEE Power Electronics Specialists Conference 77 Record, (PESC) on pages 160, et. seq.
Still further description of the prior art may be found in "Coupled-Inductor and Other Extensions of a New Optimum Topology Switching DC-to-DC Converter" by Slobodan Cuk and R. D. Middlebrook in IAS 77 Annual, pages 1110, et seq.
The authors of those papers refer to U.S. patent application Ser. No. 837,532, now U.S. Pat. No. 4,184,197, the subject matter of which is unknown to the inventors of this invention.
Cuk, et al., have described a circuit which either produces a zero ripple output current or a zero ripple input current, but not both. See "Switching DC-to-DC Converter with Zero Input Or Output Current Ripple" by S. Cuk, Proceedings of IEEE Industry Applications Society Annual Meeting, Toronto, Canada, Oct. 1-5, 1978.
The Cuk apparatus utilizes a pair of tightly coupled windings wherein the inductances may either be adjusted to cause the output current to be ripple free or to cause the input current to be ripple free. Typically the Cuk apparatus has the two closely coupled windings in series connection with an energy transfer capacitor between them. The two sides of the capacitor are alternately grounded, and the careful adjustment of inductance values and coupling coefficient causes the current through the load or the input current to be substantially ripple free.